Hello and thank you for reaching out. Currently when using skinned meshes (such as LC) on the avatar, the 3D thumbnail cannot render poses. This is a limitation of the current format being used to render those 3D thumbnails on the web. There is a longer term goal to move to a new format, but we currently do not have a timeframe for it.
Thank you for understanding and for your patience on this as we are working on bringing many exciting things to the platform